Using CIMIS or an E-pan, you end up with a number that's called Reference evapotranspiration or ETo for short. This number approximates the evapotranspiration of a field of 4 to 6 inch tall, cool-season grass that is not water stressed. To use this number to calculate water use for avocados you must multiply the ETo by a crop coefficient (Kc) that accounts for the ET difference between the avocado and the cool-season grass. Below are the crop coefficients for avocado based on research done in Corona, Ca (1988-92) and Covey Lane, North San Diego County, Ca (1992-97).
|
Months
|
Kc's
|
|
Jan
|
0.40
|
|
Feb
|
0.50
|
|
Mar
|
0.55
|
|
Apr
|
0.55
|
|
May
|
0.60
|
|
Jun
|
0.65
|
|
Jul
|
0.65
|
|
Aug
|
0.65
|
|
Sep
|
0.60
|
|
Oct
|
0.55
|
|
Nov
|
0.55
|
|
Dec
|
0.50
|
For Further Information
Irrigation Scheduling, a guide for efficient on-farm water management. University of California Division of Agriculture and Natural Resources Publication #21454. 1989.